Architectural Acoustics Acoustic study of Auditorium design in a Convention and Exhibition Centre
Report By: Sanjana Kripalani 16050
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Contents 1. Abstract .................................................................................................................................................................................6 2. Introduction ............................................................................................................................................................................7 3.Aims and Objectives ...............................................................................................................................................................8 4.Background study ...................................................................................................................................................................9 4.1 History of Acoustics ..........................................................................................................................................................9 4.2 History of Acoustics in Architecture ................................................................................................................................10 4.3 Evolution of Modern Acoustics .......................................................................................................................................14 5.Literature study .....................................................................................................................................................................15 5.1 History and Auditorium Design around the world. ..........................................................................................................15 5.2 Auditorium design details. ..............................................................................................................................................16 5.3 Auditorium planning and ancillary spaces in an auditorium. ...........................................................................................16 5.4 Base theatre design. ......................................................................................................................................................17 6.Methodolgy and Scope .........................................................................................................................................................18 6.1 Methodology ...................................................................................................................................................................18 6.2 Scope .............................................................................................................................................................................18 2
7. Data collection and observation...........................................................................................................................................19 7.1 Design of the auditorium ................................................................................................................................................19 7.2 Acoustics: Absorb, Block, and Cover .............................................................................................................................31 7.3 Acoustic Materials ..........................................................................................................................................................33 8. Case study...........................................................................................................................................................................36 8.1 Calvary Convention Centre, Kuala Lumpur ....................................................................................................................36 8.2 Experimental Theatre, Kuala Lumpur. ............................................................................................................................41 9.Research Implementation Strategies ....................................................................................................................................45 10.Findings & conclusions .......................................................................................................................................................47 11. Bibliography .......................................................................................................................................................................48 12.Acronyms............................................................................................................................................................................49 13.Appendix.............................................................................................................................................................................50
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Table of Figures Figure 1: Ancient Theatre at Greece ....................................................................................................................................................... 10 Figure 2 Roman Theatre, Turkey ............................................................................................................................................................ 11 Figure 3: Colosseum .............................................................................................................................................................................. 11 Figure 4: Theatre at Italy ........................................................................................................................................................................ 11 Figure 5: St. Marks Cathedral, Italy ........................................................................................................................................................ 12 Figure 6: Teatro Olimpico, Italy ............................................................................................................................................................... 13 Figure 7: Auditorium Site lines ................................................................................................................................................................ 19 Figure 8: Auditorium seats ...................................................................................................................................................................... 19 Figure 9: Auditorium Seat ....................................................................................................................................................................... 20 Figure 10: Centre to centre distance of seats ......................................................................................................................................... 20 Figure 11: Auditorium Seating Arrangements ......................................................................................................................................... 23 Figure 12: Vertical Sightlines .................................................................................................................................................................. 24 Figure 13: Horizontal sightlines .............................................................................................................................................................. 24 Figure 14: Basic Attached spaces to any auditorium .............................................................................................................................. 25 Figure 15: Flowchart showing movement around an auditorium ............................................................................................................. 26 Figure 16: Video comfort, sightlines ........................................................................................................................................................ 27 Figure 17: Flat surface............................................................................................................................................................................ 27 Figure 18: Concave Surface ................................................................................................................................................................... 28 Figure 19: Convex Surface ..................................................................................................................................................................... 28 Figure 20: Typical variation of RT with volume for auditoria .................................................................................................................... 29 Figure 21: Multipurpose auditoria and stage flexibility ............................................................................................................................. 30 4
Figure 22: Barrier Acoustics and treatments ........................................................................................................................................... 34 Figure 23: Working of porous absorber................................................................................................................................................... 35 Figure 24: Geometric Slcies ................................................................................................................................................................... 35 Figure 25: Plan ....................................................................................................................................................................................... 36 Figure 26: Section .................................................................................................................................................................................. 37 Figure 27: Auditorium shape and massing.............................................................................................................................................. 37 Figure 28: Auditorium Volume ................................................................................................................................................................ 38 Figure 29: Auditorium Levels .................................................................................................................................................................. 38 Figure 30: Placement of seats ................................................................................................................................................................ 39 Figure 31: Wave movement, surface layout ............................................................................................................................................ 39 Figure 32: Materials used for acoustic treatment .................................................................................................................................... 40 Figure 33: Side walls-good for reflection ................................................................................................................................................. 40 Figure 34: Ceiling-Acoustic panels and rockwool .................................................................................................................................... 40 Figure 35: Section .................................................................................................................................................................................. 41 Figure 36: Plan ....................................................................................................................................................................................... 41 Figure 37: Viewing angles ...................................................................................................................................................................... 42 Figure 38: Acoustic treatment ................................................................................................................................................................. 42 Figure 39: Sound shadow ....................................................................................................................................................................... 43 Figure 40: Materials used for acoustic treatment .................................................................................................................................... 44 Figure 41: RT for different sized rooms................................................................................................................................................... 44
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1. Abstract The topic aims to create a thorough study of how acoustics affect an Auditorium in a Convention and Exhibition Centre. The report puts forward various design challenges, strategies and ideologies that can be used to implement appropriate design solutions for enhanced user experience. The acoustics of a space can have a huge role in large scale spaces depending upon the use of the space and the users. This report answers design problems that are related to the acoustical treatment of auditoriums in detail. The report includes an analysis of various forms, materials, shapes, standards, and design techniques. Basic design understanding through this study can be very helpful in planning and design.
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2. Introduction A convention centre is a large-scale project. It consists of various spaces from small scale to large scale. Auditoriums are spaces used mainly for gatherings related to the act of listening, observing, and speaking. The design of auditorium space plays a huge role in the overall experience of a user. Every space in an auditorium needs to be looked at differently but still together in terms of architectural design and user experience together. The heights, volumes, sizes of every auditorium differ and hence needs to be looked at separately. A good design can bring different psychological feelings in users- security, comfort, affinity, concentration, etc. Acoustics relates to sound or sense of hearing. It is the study of sound. Acoustics can control the sound of any space. The study of acoustics revolves around the generation, propagation and reception of mechanical waves and vibrations. Uncomfortable, noisy spaces can have negative impacts on humans like headaches, hearing loss, low concentration, high levels of stress, etc. This study of sound can help design in order to impact users to feel comfortable and make spaces more comfortable. Acoustics and architecture together play a very important role in terms of the user. Sound can have an impact on people and so can architecture. The fusion of architecture and acoustics can be very interesting to understand keeping the end-user in mind. In a typical convention and exhibition centre, various spaces like seminar halls, ballrooms, exhibition halls, meeting spaces, conference spaces, open-air theatres, etc. are designed for all types of users that would use the centre. Auditoriums can be used to host multiple types of events. Hence, the acoustic treatment needs to be well thought of and this study will help in finding design techniques for all these spaces. Studies like acoustic materials, space and its shape, heights of spaces for better sound quality, etc. shall be studied in this report. 7
3.Aims and Objectives Aims ● To study various elements of an auditorium used in a Convention and Exhibition centre. ● The intention of this study is to understand the acoustics of an auditorium in relation to height, shape, size, volume, materials, etc.
Objectives ● To study fundamentals of sound and human perception and reactions to sound. ● To study different architectural spaces in auditoria and their role in acoustics. ● To understand various factors involved in acoustics of auditoria. ● To learn about different materials used in acoustic treatment. ● To analyse problems faced and solve them through proper design strategies. ● At last, to compile all these studies and create basic design techniques that can be helpful in the future design phase.
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4.Background study The expected footfall of users in a convention and exhibition centre can be in thousands. It consists of all sorts of spaces - small and large. Small scale-spaces like meeting rooms, conference rooms, assembly areas, passages, etc. are where the amount of footfall is less. Whereas, large scale spaces like conference halls, ballrooms, exhibition halls, seminar halls, amphitheatres, etc. are spaces that have thousands of people using them. Every space has its own character in terms of size, height, volume, usage, activity, and so on. User comfort in each space needs to be catered differently in every space. Factors like viewing angles, sound quality, thermal comfort, are few factors that make a space desirable. Study in terms of materials, viewing angles, the volume of each space in an auditorium is of great help to architects. Various acoustical problems occur but with the help of understanding the past structures and present auditorium designs, new design techniques can be evolved.
4.1 History of Acoustics The word "acoustic" is derived from the Greek word ‘akoustikos’ which means ‘of or for hearing, ready to hear’. In the early 6th century BC, the famous Greek philosopher Pythagoras thought- how does some sound seem more beautiful than the others. He found answers to this question in terms of harmonic waves on a string. He observed various lengths of vibrating strings and found that it is expressible in a ratio of integers where the sound is better if the ratio is smaller. He discovered the first 6 overtones of a vibrating string. Aristotle understood that the sound consists of a movement in the air resulting in the nature of waves. 9
In 20 BC, Romanian architects wrote about architectural acoustics. He compared sound waves to be similar to water waves but in a three-dimensional manner where, if a sound is disrupted because of obstructions, it will flow back or break off the waves. He described that the ascending seating in ancient roman theatres was to avoid disruption of sound. Also, copper pots would be placed on upper tiers so that sound quality is maintained. Later in the 1800s, Scientists like Galileo discovered all the laws of vibrating strings. Various experiments were conducted on speed and sound. Later, in the late 1600s Newton discovered the relationship for wave velocity.
4.2 History of Acoustics in Architecture Architectural acoustics can be of a room or a building or any space in general. It can help with good speech communication in various spaces. Good acoustics can make a space more effective by making a comfortable area for the users. Acoustic discomfort can cause a lot of harm. Greeks: Ancient Greek and Roman architecture are known for open-air theatres. They located the audience as close as possible to the elevated stage by shaping the steeply banked seating area in a semi-circle which naturally resulted in reason-ably good hearing. Later the Romans built large slanting roofs above which proved to be efficient sound reflectors. The Greeks, perhaps due to their democratic form of government, built some of the earliest outdoor
Figure 1: Ancient Theatre at Greece
amphitheaters. The seating plan was in the shape of a segment of a circle, slightly more than 180◦, often on the side of a hill
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facing the sea. The seating was steeply sloped in these structures, which had good sight lines. It is remarkable that this theater, which seated as many as 17,000 people, actually functioned.
Romans: The Roman and the late Hellenistic amphitheaters followed the earlier Greek seating pattern, but limited the seating arc to 180degrees. They also added a stage house behind the actors, a raised acting area, and hung awnings overhead to shade the patrons. The chorus spoke from a hard-surfaced circle (orchestra) at the center of the audience. The most impressive of the Roman amphitheaters was built between AD 70
Figure 3: Colosseum
and 81, and was later called the Colosseum.
Early Christian Period and Gothic Cathedrals: It was an amalgam of the Roman basilica (hall of justice) and the Romanesque style that led to the design of churches. The basic design
Figure 2 Roman Theatre, Turkey
consisting of naive, atrium, high ceilings became popular - there were 31 Basilican churches in Rome alone.
Figure 4: Theatre at Italy
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These massive structures served as focal points for worship and repositories for the religious relics that, following the return of the crusaders from the holy lands, became important centers of the valuable pilgrim trade. It was mainly used for music and religious purposes.
Renaissance Churches: The great outpouring of art, commerce, and discovery that was later described as the Renaissance or rebirth, first started in northern Italy and gradually spread to the rest of Europe. The development of new music during these years was rich and profuse. Thousands of pieces were composed and people got together in these churches.
Baroque Churches and Renaissance theatres: Figure 5: St. Marks Cathedral, Italy
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During the Classical period of Mozart and Beethoven, Music pieces were composed in formal halls. Orchestras and concerts became a thing then. ‘Altes Gewandhaus’ is a structure in Germany that seated about 400 people with the orchestra located on a raised platform at one end occupying about one quarter of the floor space. The room had a reverberation time of about Figure 6: Teatro Olimpico, Italy
1.3 seconds and was lined with wood paneling, which reduced the bass build up.
Shoebox Halls: Several orchestral halls were constructed in the late eighteenth and early nineteenth centuries that were known for their fine acoustics and for their influence on later buildings. They are all of the shoebox type with high ceilings, multiple diffusing surfaces, and a relatively low seating capacity. The oldest is the ‘Stadt Casino in Basel’ in Switzerland, which was completed in 1776. 13
4.3 Evolution of Modern Acoustics In the 19th century, the beginning of acoustics as a science study started. Books were written and experiments were carried out. The planning of the Boston Music Hall, now called Symphony Hall, was made using a shoebox shape and heavy plaster construction with a modest ceiling height to maintain a reverberation time of 1.8 seconds. Narrow side and rear balconies were used to avoid shadow zones. The stage was enclosed with angled walls and ceiling for better sound. The deeply coffered ceiling and wall niches containing classical statuary helped provide excellent diffusion.
In the 20th century, the development of electroacoustic devices like microphones, amplifiers, loudspeakers, and other electronic instruments flourished. The precision, which is now available in the ability to record and reproduce sound, has created an excellent experience for the user that is difficult to match in a live performance. With more knowledge on acoustical materials, and other acoustic related studies design just keeps getting better by the day.
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5.Literature study 5.1 History and Auditorium Design around the world. Barron, M. (2010). Auditorium Acoustics and Architectural Design. 2 Park Square, Milton Park, Abingdon, Oxon OX14 4RN. Spon Press. In this study, the author describes Auditorium acoustics in detail. The book consists of a detailed analysis of various definitions related to acoustics and architectural acoustics. Also, it contains broad information about absorption of sound in relation to various examples of structures in the past.
The author talks about various definitions that play an important role in architectural acoustics. Sound and rooms are the major elements where he talks about sound propagation, reflections, and acoustical defects. Acoustics in symphony concert halls and the development of these halls with respect to size, volume, form, modelling, diffusion solutions and how a fan shape hall can work in most cases. He describes case studies of various concert halls in Britain. Barron also emphasizes on acoustics in speech- How open-air theatres work while understanding aspects of speech. Acoustics for theatres, operas and multipurpose uses consists of multiple elements of acoustics and space that work hand in hand.
The author recommends multiple aspects of architecture design in auditoria acoustics for multipurpose uses.
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5.2 Auditorium design details. Long, M. (2006). Architectural Acoustics. USA. Elsevier Academic Press. In this book, the author talks about multiple aspects of architecture design in terms of acoustics. This study plays a crucial role in building this topic research. The author talks about various fundamentals involved in acoustics- history, definitions, human perceptions to different spaces and sounds. He focuses on sound in terms of surfaces and sounds in enclosed spaces and multiple sound systems. Sound attenuation takes place in ducts, and mechanical systems. The author talks about various environmental noises like aircraft and traffic noise and how these noises affect sound quality inside the spaces. He also emphasizes on the design criteria for multipurpose auditoria and sanctuaries that cover areas like shape, size, capacity, etc.
This study helps in understanding the specialized design problems in walls, ceilings, platforms, pit design and their solutions.
5.3 Auditorium planning and ancillary spaces in an auditorium. Adler, D. (1999). Architectural Acoustics Metric Handbook Planning and Design Data. Oxford. Architectural Press. This book consists of multiple sections. The first section that is useful for this research is about Auditoria by Ian Appleton and Joe Aveline. In this book, they have done a detailed study of the planning aspects of auditoria. A detailed study about seating, access, auditorium design in terms of shape, size, sight lines, furniture, escape routes, handrails, etc. Theatres, studio theatres, concert halls, conference rooms, multipurpose auditoria, and other support facilities have been detailed out in terms of planning. 16
Also, details about stage planning and related spaces like changing rooms, scene docks, loading bays, equipment for sound and lighting, etc. They have recommended solutions to design restraints in terms of auditorium design and planning. The other section focuses on community centres and their design by Jim Tanner, who very well expresses elements of design in community centres where he focuses on barrier free design elements for everyone- elderly, disabled, children of all ages and so on. Areas such as halls, entrances, kitchen, toilets, storage, furniture are some areas where he has shed some light. Both these sections help in learning more about auditoria and considering every minute details along with spatial planning of ancillary activities in the convention and exhibition centre which is for a community.
5.4 Base theatre design. Harris Group Inc, Base Theatre Design Standards.
This article talks about how functional diversity, building exteriors, auditoria with backstage support in an air combat command at Virginia, USA work. It consists of information on the capacity of people and space design standards accordingly. It has calculations done by experts, catchment area drawings, exit requirements, ceiling configurations, curtains, stage panels, etc. Also, a very detailed material study has been done explaining finishes from paint, tiles, wall coverings, ceilings, etc.
This study shall help me review materials used and get information for 500-1000 capacity seating in an auditorium.
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6.Methodolgy and Scope 6.1 Methodology This study of the report, its findings and recommendations shall use multiple aspects of previous studies done by great scholars in the field. Multiple factors are necessary to examine the several design ideas of auditoria, which vary in most cases due to multiple approaches. The core methodologies used in generating the data underlying the findings of this report are: research from papers and books, review of these studies and other relevant literature, and case studies found online. With the help of quantitative and qualitative data available online and through books, the research is a cumulative data collected by various other people. The data is collected through gathering observations.
6.2 Scope The scope of this study is to understand Auditorium Acoustic and how it works in a convention and exhibition centre. This study shall glance through aspects related to form, shape, volume, materials, size, etc. of an auditorium. It shall also help in providing innovative design techniques
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7. Data collection and observation 7.1 Design of the auditorium The three-dimensional volume of an auditorium is conditioned by the need for all members of the audience to be able to see the whole of the platform or stage and to hear the actor, singer, musician or speaker. Seating density, floor rake and seating layout are partly determined by this, partly to give the audience an appropriate level of comfort and also to ensure means of escape in an emergency, such as a fire, within the time required by safety considerations.
Design of the auditorium seat: Auditorium seats should be of appropriate standard of comfort. The range of human body dimensions is wide, while in most auditoriums a single size of seat is provided, the tolerance levels vary from person to person. Young people can tolerate simple seating which can be
Figure 7: Auditorium Site lines
less comfortable by older people. Those attending sessions that are long in duration, expect more comfortable seating. Seats are generally designed for the average person expected to use it. Minor variation is achieved by the upholstery and adjustment of the back and seat pan material when the seat is occupied: otherwise the seat selection is a common size within the whole auditorium layout. Figure 8: Auditorium seats
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Seat Dimensions: •
Minimum width of seats: 500mm with armrest.
•
Seat height: 430-450 mm
•
Seat inclination: 7-9°
•
Back height: 800–850 mm above floor level
•
Seat depth: 600–720 mm
•
Arm rests: 50 mm minimum width
•
Acoustics: Upholstery to satisfy the acoustic requirements, usually the level of
Figure 9: Auditorium Seat
absorbency when unoccupied.
Seat Supports: The permanent fixing of a seat can be: ● Side supports shared by adjacent seats ● A pedestal or single vertical support ● Cantilevered brackets fixed to riser (if of sufficient height) and ● shared by adjacent seats or ● A
bar supporting a
group
of seats with
leg
or bracket
support Figure 10: Centre to centre distance of seats
Wired services: 20
These may be required for conference use. They can be incorporated into the arm of the seat or into the rear of the seat or table in front. For music, drama and cinema there may be provision for earphones for people with hearing impairment, or this facility may be provided by an induction loop. Every member of the audience should be able to see and hear clearly whatever is happening on every part of the stage or platform. A clear view for every one of the main parts of the stage or platform is normally achievable in modern auditoria. Every person in the audience should be able to see and hear everything that is happening on the stage clearly.
Visual limitations: determine the maximum distance from stage to the audience. The audience should be able to watch and experience performances with ease. This distance varies according to function type and the scale of the performance: ● For drama it is essential to see facial expressions, and the maximum distance should be 20 m ● For opera and musicals, facial expressions are less critical and the distance can be 30 m. ● For dance the audience needs to appreciate the whole body of dancers and facial expression,the distance should not exceed 20 m. ● For full symphonic concerts acoustic conditions predominate. ● For chamber concerts acoustic conditions also predominate but visual definition assists achieving an intimate setting. ● For conferences, speakers and lecturers there are two scales: small scale to see facial expressions, restricted by 20 m, larger scale where facial expression is not crucial -30m. ●
For slide, video, television and overhead projection visual limitations are determined according to the technologies.
Aural limitations: 21
This refers to the distances across which speech, singing and music can be clearly heard without the need for amplification, and beyond which they cannot. For drama, opera and classical music amplification is deprecated but it is acceptable for variety and pantomime and essential for rock music. For amplified sound the auditorium requires a dead acoustic with no reflected sound from the platform or stage and limited or no reverberation; loudspeakers are positioned to provide full and even coverage of the audience. The volume and quality of the unamplified sound is dependent on the volume, shape, size and internal finishes of the auditorium, and on its resultant reverberation time. It is therefore not possible to lay down limits as for visual appreciation. Even experts in acoustics find that their predictions are not always borne out in practice, although they should be consulted and their advice followed wherever possible. It has been found feasible to improve the acoustics of existing auditoriums.
Gangways: As gangways are essential escape routes, their widths are determined by the number of seats served. The minimum is 1100 mm. They can be ramped up to 10%, but only 8.5% if likely to be used by people in wheelchairs. If the seating rake is steeper, gangways must have steps extending the full width and these must have consistent treads and risers in each run. This means that the row-to-row spacing and row rise should be compatible with a convenient gangway tread and riser; and this in turn means that the shallow curve produced by sightline calculations should be adjusted to a straight line.
Levels in the auditorium: With a single level only, the pitch of the rake requires particular attention to achieve a sense of enclosure. The Greek Amphitheatre is the exemplar. Seating capacity within aural and visual limitations can be increased by the addition of one or more balconies within the overall permissible volume of the auditorium. Similarly, boxes, side galleries and loges can be added to the side walls, especially in the case of the proscenium format.
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Seating geometry: Seating is usually laid out in straight or curved rows focused towards the platform or stage. Further forms are the angled row, straight row with curved change of direction and straight rows within emphasized blocks of seats,
Number of seats in a row: With traditional seating the maximum number is 22 if there are gangways at both ends of the row, and 11 for gangways at one end.
Seating density :Seats with arms and tippable seats can occupy a space as small as 500 mm wide (less for seats without arms) with a row-to-row dimension of 760 mm, but can be as large as 750 mm wide by 1400 mm. The area per seat therefore varies between 0.38m2 and 3.05m2. Increased dimensions reduce seating capacity. Minimum dimensions as laid down by legislation offer a low standard of comfort and should not be taken as a norm, but the social cohesion of the audience may be lost if the standards are too high. In conference halls where writing space is required, lower densities are inevitable.
Sightlines for a seated audience should be uninterrupted by any overhangs or other peoples’ heads. The auditorium Figure 11: Auditorium Seating Arrangements
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needs to be designed according to certain limitations set by vertical and horizontal sightlines.
Vertical sightlines can be calculated by establishing: P Lowest and nearest point of sight on the platform or stage for the audience to see clearly. HD Horizontal distance between the eyes of the seated members of the audience, which relates to the row spacing and can vary from 760 mm to 1150 mm and more. EH Average eye height at 1120 mm above the theoretical floor level: the actual eye point will depend on seat dimensions.
Figure 12: Vertical Sightlines
E Distance from the centre of the eye to the top of the head, taken as 100 mm as a minimum dimension for the calculations of sightlines. For assurance that there is a clear view over the heads of those in the row in front this dimension should be at least 125 mm. D Front row of seats: the distance from point P to the edge of the average member of the audience in the front row. The relationship is shown in the figure below. This gives every member of the audience similar viewing conditions. This may be reduced to a single angle or series of angles. Horizontal sightlines: Given a particular size and shape of the platform or stage, horizontal sightlines limit the width of the seating area in the 24
Figure 13: Horizontal sightlines
auditorium. This is more critical with the proscenium stage and with film, video and slide projection. Without head movement, the arc to view the whole platform or stage on plan is 40° from the eye.
Other spaces for actors, singers and dancers dressing rooms, audience, etc are behind/around the auditorium. Arrangements are illustrated in the figure, covering single shared and communal occupancy rooms. ● Green room with kitchen and servery: 3.4m2 per occupant. ● Laundry for repair and maintenance of costumes, 20m2 minimum. ● Costume store, including skips and rails Costume delivery. ● Specialist make-up room: 10 m2 minimum per person. ● Pre-performance practice room(s) (singers): 15 m2 minimum. ● Pre-performance dance studio (dancers): 1000 m2 minimum. ● Physiotherapy room (dancers): 15 m2 minimum. ● Wig store and hairdresser’s room: 5–10m4. ● Waiting area for visitors and dressers. ● Offices: children’s supervisor, company manager, touring Figure 14: Basic Attached spaces to any auditorium
manager, etc. 10m2 minimum per office. ● Toilets. ●
Performers’ assembly areas: at points of entry to stage.
● Box office 25
● Preparation room, press room, etc
Lighting control room: This is a limited requirement for conferences, but lighting control could be incorporated into a projection room at the rear of the auditorium, minimum size 2 m to 3.5 m.
Sound control room in this case an open room preferably at rear of the auditorium adjacent to the lighting control room, minimum size 2 m to 3.5 m.
Screens: Increasingly, back-projection screens are being used. In this case the projection room will be behind the platform rather than behind the audience. Back projection for video, film and slide requires wide-angle lenses but allows more freedom for speaker
Figure 15: Flowchart showing movement around an auditorium
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Slide projection: High-intensity projectors allow some light in auditorium for note taking. Screen areas for projecting slides should be square, as slides may be in portrait or landscape format. For three-screen projection the side screens are sometimes angled as much as 30° from the centre screen
Video projection Video projectors are now usually mounted at high level in the auditorium, on stands or behind the screen. Close-range projectors can produce pictures up to 3 m high; they should be 3.5 to 3.6 times the picture width from the screen. Video cassettes may be loaded in a projection room. For a large screen a long-range projector is used producing a picture up
Figure 16: Video comfort, sightlines
to 7.5 m high. It should be housed in a projection room, with room for control and back-up equipment consisting of racks for VCR equipment, monitor screens, off-air times and ancillary control unit.
Acoustics for films: Cinemas are now equipped with stereophonic sound systems which require acoustically dead auditoria. The ideal is a zero-reverberation time. Hence all finishes – floor, walls, ceiling and seats – need to be sound absorbent. Side walls should not be parallel, and a fan shape is preferred. The auditorium should be structurally and enclosure wise insulated from external noise. A suitable ambient noise standard for cinemas is NR30 to NR35.
Sound is reflected in different ways depending on the shape of the reflecting surface: Flat Surfaces:
Figure 17: Flat surface
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A flat surface is effective in distributing sound. If the surface is large enough and positioned correctly, a flat surface can project sound toward the listeners. Flat surfaces can also cause problems like flutter echo if placed incorrectly.
Concave surfaces: Concave surfaces cause reflections to be concentrated rather than dispersed. This causes an abundance of reflection to be heard by the listeners. Reflections can also bring delayed reflections around the room.
Convex surfaces: Convex surfaces are the best surfaces for distributing sound. They provide a wide spread of reflected sound. Reflections can be controlled through room shaping as described above, irregularities within the
Figure 18: Concave Surface
room such as columns, trusses, surface undulations, etc., or through the use of absorptive materials (those with a high NRC.)
Figure 19: Convex Surface
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Reverberation Time (RT): RT is design factor for acoustics in an auditorium. People have multiple opinions as to what the optimal RT should be. The RT for speech and recorded music should be as short as possible, as one is only interested in the direct and not the reverberant sound; for light music they should be short and for concert and church music they should be long. By measuring the reverberation times in auditoria which are considered to possess good acoustic qualities, one can arrive at a relationship between the "optimum'' reverberation time for a particular use and the volume of the auditorium. For a multipurpose auditorium, it should be between 0.5 to 1.5
Figure 20: Typical variation of RT with volume for auditoria
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Multipurpose Auditoriums:
As seen in the adjoining images, A multipurpose auditorium can be used in multiple ways just by changing the way function of the stage by using acoustical barriers/shells. For example, •
An orchestra needs space for the choir to assemble.
•
For an opera or dance event, a wide proscenium is needed.
•
For a jazz performance, there should be a proper strip of standing area.
•
In the case of a drama event, the stage is reduced to a smaller area.
•
For conferences and talks, the stage is very small and a projection screen is installed.
•
For cinema, a screen and speakers are installed, again, making the stage smaller in size.
Figure 21: Multipurpose auditoria and stage flexibility
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7.2 Acoustics: Absorb, Block, and Cover A balanced acoustic design absorbs, blocks, and covers (the ABCs of acoustics) sound. This can be achieved by employing sound masking technology and installing interior products with acoustic properties. 1. Absorb Sound The most direct way to address the control of unwanted noise within a space is to properly treat its shell (floor, ceiling, and walls). A room filled with hard finishes can cause echoes and reverberation sound and can make communication difficult. To eliminate these problems, products and systems with sound-absorbing characteristics should be carried out. These porous/fibrous sound-absorbing materials soak up sound waves by trapping them in an internal maze of air pockets.
Ceilings can absorb sound and they can control sound in other ways as well. They can also be used to deflect or distribute sound more evenly throughout a space. The NRC rating is between 0 and 1. To absorb more, the NRC rating should be higher. Certain materials are more noise absorbent - for instance, fiber glass has a high NRC. Ceilings should have closure/seal components to prevent sound leaks through return-air grills, lay-in light fixtures, sprinkler heads, and other utility penetrations.
Installation of carpets with cushioning has numerous advantages that includes the absorption of airborne sound and reduced footfall noise. Also, a carpet helps to create an aesthetic ambiance conducive to lowered voices, a heightened sense of privacy, and reduced distractions. Polyurethane cushion-backed carpet has a higher NRC rating when compared to bare concrete and
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conventional jute-backed carpet. Cut-pile (vs. loop pile) carpet with a permeable carpet backing laid over cushion has higher NRC ratings.
2. Block Sound Sound absorption is just one way to improve acoustics, blocking sound from spreading into adjacent areas is equally important. Both walls and carpet block sound transmission. The best sound absorption relies on lightweight, porous materials, the best sound-blocking materials (solid masonite, metal, or hardboard) are dense and heavy. With no air spaces for sound waves to slip into and through, panels containing these tightly packed interiors essentially cut off the direct path into adjacent spaces. These divider panels can be extremely effective at blocking and absorbing sound simultaneously. To be effective at both and provide non-intrusive levels of speech privacy, the panel should meet the following criteria •
Panel heights should be a minimum of 60 inches; 72 inches is preferred.
•
The recommended NRC is 0.60.
•
A Sound Transmission Class (STC) rating between 18 and 20 is ideal.
Panels should be high enough to block conversational noise from traveling over the top of partitions into adjacent spaces. The higher the panel, the sounder the blocking is. Sound-blocking benefits level off in panels that are 75 inches or higher.
3. Cover Sound Instead of eliminating noise, environments should have a mixture of noises than complete silence. Even the slightest of sounds will be heard, if there isn’t any ambient noise. After the interior shell is equipped with products that absorb and block sound, 32
the final step is to cover the sound with masking technology. The sound masking system slightly raises the overall structure’s sound level, covering or dampening the sound of a typical conversation. The sound emitted by the masking system is similar to that produced by HVAC equipment – HVAC equipment emits sounds that are evenly distributed.
The system consists of a set of electronic components and speakers, and can be installed above a suspended ceiling system, pendant-mounted in areas with open ceilings, or placed under access flooring. Sound masking systems provide benefits in most indoor, non-industrial spaces. Once the system has been purchased and installed, it is tuned to a specific frequency. Tuning should take place after the space is fitted out, but before occupation. The best tuning capabilities will adjust the spectrum of the masking sound being emitted to the specific acoustical signature or physics of the individual room. Good acoustical performance requires a balanced approach of absorption, physical barriers, and sound masking.
7.3 Acoustic Materials Barrier Materials •
Barriers must be nonporous—that is, they must block the passage of air through them.
•
They must have sufficient mass so that the sound traveling through the barrier is significantly less than the sound diffracting over or around the barrier. Barriers should be built of a material having a total surface mass density of at least 20 kg/sq. m
•
They must be weather resistant and properly designed to withstand wind and other structural loads appropriate for the location. 33
•
The mass requirement can be fulfilled using a support structure with one layer of 16 mm and one layer of 19 mm plywood sandwiched. When the panels are applied to both sides of a stud, 90 mm wide, they may be less massive, typically 13 mm to 16 mm plywood. Virtually any thickness of concrete or concrete masonry unit that is self-supporting will meet the mass requirement.
•
A stucco wall is very effective. Stucco is 22 mm thick
•
Precast concrete panels, treated to look like wood or brick and supported by I beam columns, are commercially available. The panels are held in place at their ends by the flange of the I beam.
•
Corrugated sheet metal panels sometimes are used to construct noise barriers.
•
Commercial barriers with both solid and sound-absorbing perforated skins are available, usually in 18 Ga. steel supported by steel columns.
•
Absorbing materials such as fiberglass can be incorporated behind the perforated panels to reduce barrier reflections. The fiberglass is encased in a plastic bag to protect it from the weather.
•
Noise barriers should be constructed so that there are no openings between the barrier and the ground. Openings allow the sound to pass under the barrier and can reduce its effectiveness. 34
Figure 22: Barrier Acoustics and treatments
•
Trees, shrubs, and other foliage are not effective. They are porous and do not meet the mass requirement. Rows of trees, heavy grass, and dense foliage can provide some excess ground attenuation. They are also useful in giving a psychological sense of privacy, or in landscaping a sound barrier to make it more aesthetically acceptable.
Absorptive materials, such as acoustical ceiling tile, wall panels, and other porous absorbers are often characterized by their NRC, rounded to the nearest 0.05. Porous Absorbers: Several mechanisms contribute to the absorption of sound by porous materials. Air motion induced by the sound wave occurs in between fibers or particles. At low frequencies absorption occurs because fibers are relatively efficient conductors of heat. Practical Considerations in Porous Absorbers: For most architectural applications, •
A 1” (25 mm) thick absorbent fiberglass panel applied over a hard surface is the
Figure 23: Working of porous absorber
minimum necessary to control reverberation for speech intelligibility. •
Some localized effects such as high-frequency flutter echoes can be reduced using thinner materials such as (5 mm) wall fabric or (6 mm) carpet, but these materials are not thick enough for general applications.
•
If low-frequency energy in the 125 Hz. octave band is of concern, then at least 2” (50 mm) panels are necessary. At even lower frequencies, 63 Hz and below, panel absorbers such as a gypboard wall.
•
Figure 24: Geometric Slcies
Geometric shapes used as diffusors. The two best diffusor geometries are “slices” or sections of cylindrical and spherical shapes, because they evenly spread sound energy within a space. 35
8. Case study 8.1 Calvary Convention Centre, Kuala Lumpur (Ref: Jinsunfoo) Total built up area: 600,000 sq. Ft Completed in: 2013 Type of Auditorium: Multipurpose Auditorium Total seats: 5000
The Calvary Convention Centre (CCC) is a distinctive convention centre that is dedicated to the pursuit of holistic activities. These activities include the hosting of international and local conventions, services, seminars and creative arts productions, not to mention the provision of educational, spiritual and vocational development for the Malaysian public, especially its youth. The 6-storey complex designed by T.R Hamzah & Yeang Sdn Bhd houses a variety of facilities including an auditorium, theatrettes and a multi-purpose banquet hall. Located on a 4.9-acre piece of land in Bukit Jalil, the CCC occupies a total built up area of about 600,000 sq. ft. The massive 5,000 seat auditorium is fan-shaped, suitable for great audience capacities. Two main trusses support the hall roof, each supported by two mega Figure 25: Plan
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columns. Sixty metres of column-free space spans within the auditorium, providing an unobstructed view of the stage throughout the hall. The auditorium was designed to be a single-tiered floor allowing unobstructed circulation from the back of the hall to the stage in front. It has multiple features that allow the auditorium to be modified to suit different functions and events. The hall is equipped with built-in structures for the future installation of foldable partitions that divide the auditorium into three smaller halls that may be used for smaller functions. The front seats of the halls are retractable so that the space can be used as a speaker area when needed. The
Figure 26: Section
splayed side walls of the fan-shaped hall allow for a greater seating area that is close to the stage, and can also effectively reflect sound energy to the rear of the hall.
Auditorium Shape and Massing: The shape of the auditorium is a unique variation of the horseshoe-type hall with a combination of both curved and flat walls. The walls are flat at the front of the hall but gradually curve into a concave shape as it leads to the rear. The concave shape of the walls reflects the sound waves back into areas with less exposure to the sound source. However, the wall parallel to the stage at the back of the hall is flat instead of curved like in most horseshoe-type auditoriums.
Figure 27: Auditorium shape and massing
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Volume: The optimum size of the auditorium depends on the function of the hall and the audience capacity. Larger volumes generally produce better acoustics for music productions as the reverberation time would be longer. However, longer reverberation times are unsuitable for speakers’ areas as the voices will sound murky and unclear. Therefore, it is important to identify the most suitable volume to satisfy the specific needs of the auditorium. Although the CCC auditorium is built to accommodate a large audience capacity, the sound absorbent materials effectively brought down the
Figure 28: Auditorium Volume
reverberation time to 0.9 seconds which is suitable for speeches. The volume is - 39136.60m³
Levelling of Stages and Seats: Correct levelling of the auditorium seats ensures that sound waves reach all the occupants of the auditorium without obstruction. The seats configuration of the CCC auditorium is very effective in bridging the relationship between the audience and the speaker on the stage. Raked seats increase the volume and clarity of sound especially for audience members sitting near the back. This is due to the elimination of any interruption of sound waves caused by diffusion or absorption of the waves by obstructions. The figure shows the seat arrangement of CCC auditorium to ensure optimal sound Figure 29: Auditorium Levels
travel to all audiences. 38
Seating Arrangement: The seating arrangement in the auditorium is in a fan-shaped configuration to allow greater seating area that is closer to the stage. This allows louder and clearer sound quality to be heard throughout the hall. Since sound travels in spherical waves, the fan-shaped configuration succeeds in achieving the most effective acoustic quality. This configuration also decreases the chance of sound waves being affected by obstructions as compared to shoebox type halls. The figure shows the fan-shaped seat arrangement.
Layout of Boundary Surface: The auditorium implements a combination of concave shaped
Figure 30: Placement of seats
and stepped ceiling systems that reflect the sound back down to the audience. The concave shape also helps concentrate the sound intensity and increase the volume of the sound as it travels towards the audience. Flutter echoes are noticeable on stage as the ceiling is parallel to the floor. The figure shows the expected sound reflection from ceiling reflector panels to all audiences.
Figure 31: Wave movement, surface layout
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Materials and Properties: The materials can be divided into absorbent or reflector depending on their NRC rating, where most reflective in 0 and most absorbent is 1. Materials used here are Upholstery for the theatre seats, rockwool on the walls, plywood, plasterboard ceiling, heavy curtains, thick piled carpet on the flooring and timber flooring on the stage. Timber flooring reduces noise transmission, acoustic material under the flooring absorbs sound waves and reduces vibrations. Carpet is an outstanding sound absorber, recues footstep noise on the steps. The walls reflect and concentrate sound waves. As the volume of the space is so large,
Figure 32: Materials used for acoustic treatment
the wall is treated with fabric, followed by sponge, plywood, rock wool. The ceiling is suspended, stepped and made up of gypsum. The smooth surface helps in sound reflection. Sound: For a speech-based auditorium, any sound delay above a 40ms is an echo. The Reverberation time of this auditorium is 0.9s.
Conclusion: The Calvary Convention Centre has the flexibility to cater to both musical
Figure 33: Side walls-good for reflection
and speech-based performances. It is a multipurpose auditorium in a tropical region. Isolation by airgaps and insulation prevents outdoor noise. Smart choice of materials aids noise control and creates a suitable environment. It has an optimum RT of 0.9s for a speech-based auditorium. Figure 34: Ceiling-Acoustic panels and rockwool
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8.2 Experimental Theatre, Kuala Lumpur. A theatre located in the University of Malaya, Kuala Lumpur.
Figure 36: Plan
Figure 35: Section
The auditorium is rectangular horse shoe with a fan shape. It consists of a 3.5m wide gallery running over the last few rows of seats. It two hard side walls that reflect sound to the end, concrete side walls that reflect sound, and a back wall that is an absorbing surface. 41
The entire auditorium consists of entrance, washrooms, performance stage, backroom/backstage, VIP entrance lobby, lift lobby, balcony/galley, backstage control room.
Seats: The seats are placed in a concentric arc segment of a circle. They are at an angle of 140degrees. The distance between source at the stage and the last row of the auditorium is 22.5m. The slope of the theatre is 8 degrees, this not only provides good sidelines but also prevents direct blockage of
Figure 37: Viewing angles
sound.
Vertical elements: Zig zag small sections of dry wall and acoustic wall panels create a reflecting surface. Pointy edges on the same increase the scattering and reduce the glare.
Ceiling: The ceiling is plastered with white paint; it has curved edges that propagate better sound dispersion to the balcony seat. The ceiling cannot be too high as it causes late reflections. In this case, the ceiling is designed in small increments with sloped angles causing the ceiling itself to be a reflecting surface. Time Delay: The reflected sound reinforces direct sound if time delay is within 30m/sec. Time delay greater than 40m/s for speech-based auditoriums while, greater than 42
Figure 38: Acoustic treatment
100m/s in case of music-based auditoriums causes echo. The time delay in this project is high, therefore, the rear walls are made the main absorbing material.
Sound shadow: The region concentrated mainly in the settings beneath the gallery experiences the sound shadow. This is because of two main reasons- the distance between the sound source and the last row of seats is too much and the region lies below the gallery causing a difference of 4-5dB, the solution to this is, installing speakers in the last tier of seats on the ground floor.
Materials used: As concrete is highly reflective, a 20mm thick polished timber is installed over it causing greater sound absorption. The back wall is treated with acoustic fabric fiberglass panels and the ceiling is plastered for sound dispersion. Velour acoustic curtains are used backstage. These curtains reduce outdoor noise as well as back stage noise by reducing damper sound waves. Pleated curtains are used that have deep pleats. These pleats ensure more sound Figure 39: Sound shadow
absorption.
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Seats are upholstered with polyurethane foam which is good for absorbing sounds of high frequency. Medium pile carpet is used to absorb the impact of footstep noise.
Conclusion: The reverberation time of the auditorium is 1.4s. As it is a high-volume structure, it can be used for both music and speech making it a multipurpose auditorium. Application of acoustics in architecture is very important. Performance should be well and users
Figure 40: Materials used for acoustic treatment
should be comfortable. Every material, form, textile used impacts sound quality. Proper design strategies must be taken into consideration.
Figure 41: RT for different sized rooms
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9.Research Implementation Strategies The project site is located in Bengaluru, Karnataka. It is situated right next to the Kempegowda International Airport. The site area is approximately 35 acres. Since the site is next to an airport, outdoor traffic noise as well as aircraft noise shall be a problem. Also, the site is in a moderate climatic zone, having cool winters and not very hot summers. The tender requires a seating space of 6000 people. A regular ballroom would not be enough to accommodate that amount of traffic. It could accommodate that many people, but the quality of interaction, the speech and the sound quality reaching the audience would not be enough. Also, 6000 people sitting on one floor level makes it impossible for someone in the back to look at what is happening on the front stage. Hence, a multipurpose auditorium would be ideal to hold that capacity of people all at once which can be used for multiple events, be it for music, speeches, etc.
Strategies for outdoor noise control: •
Outdoor noise shall be Aircraft noise as well as traffic noise. For this, it is important to place the auditorium in a way such that it is away from main roads and at the same time, covered from the aircraft noise.
•
This is possible if the structure of the auditorium is properly insulated without leaving any airgaps for the sound to penetrate inside the auditorium.
•
Interior materials like heavy pleated curtains, properly plastered ceilings with proper highly insulated materials like fiberglass, rockwool, glass wool, etc. can help keep the outdoor noise.
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Strategies for better indoor sound quality: •
According to the three main principles Absorb, Block and Cover, it is important to do the same when it comes to auditorium acoustics.
•
The shape and volume of the auditorium plays an important role. Shapes like horse shoe, fan shape, shoebox are the most used shapes for auditoriums. Having slightly curved walls and walls that are not parallel to each other can be better than having all parallel walls. The volume of the auditorium should be properly thought of. If the volume is too much, it can be bad for when a speech is being performed. Whereas, it is great for a musical performance as it increases the RT.
•
Upholstered seating materials are ideal as they are good sound absorbers. The angle from the source that is the speaker and the seats should be 140 degrees. Ideally, the seats should be sloping from 8-10 degrees.
•
In order to reflect sound properly in the back of the auditorium, proper ceiling and false ceiling is required. Ceilings can either be constructed in different angles and curves to reflect sound or false ceiling materials like acoustic panels, concrete panels, concave and convex sound diffusing tiles, etc.
•
The walls can be absorbing or reflecting. If the auditorium is too large, the end walls can be absorbing while the side walls can be reflecting. Depending on this, absorbing wall materials like fibre glass fabric, hardwood timber panels, etc. Dry walls, gypsum sheets, can be used for reflecting/ avoiding flutter echoes. Porous absorbers are the most common type of absorbers. Mineral wools, synthetic foams, and felts are all examples of porous absorbers
•
The flooring used for the stage is usually timber floor so that the amount of noise created is less. In the other parts of the auditorium, the floor is covered with heavy carpet. This helps in avoiding footstep noises of the users.
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10.Findings & conclusions Herein, a new auditorium design process involving different types of materials, shapes and types of auditoriums and multiple aspects of an auditorium from an architect’s perspective for designing are understood. Several conclusions can be drawn from this research:
1) Different auditoriums need to be designed in different ways depending on the type of activity and the number of people. 2) Acoustics can be dealt with at a construction stage first, thinking about materials for insulation, roof and ceiling desing before hand can help design an auditorium better. 3) The shape and size of an auditorium plays a vital role, also the placement of seats, their levels, etc are an important aspect which comes while designing it. 4) Acoustics of an auditorium can be enhanced using technology like powerful speakers, mikes, etc. but the major role is played by the acoustic treatments done in the space(interiors). Interior materials and acoustic treatments depending on the volume, number of people, etc. By using the new computation technology available and also with the help of acoustic professionals, architects can come up with great multipurpose designs. 5) A multipurpose auditorium can be used for multiple events just by adjusting the stage and designing, keeping RT in mind.
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11. Bibliography 1. Barron, M. (2010). Auditorium Acoustics and Architectural Design. 2 Park Square, Milton Park, Abingdon, Oxon OX14 4RN. Spon Press.
2. Long, M. (2006). Architectural Acoustics. USA. Elsevier Academic Press. 3. Adler, D. (1999). Architectural Acoustics Metric Handbook Planning and Design Data. Oxford. Architectural Press.
4. Harris Group Inc, Base Theatre Design Standards. 5. (2014). Acoustic Reflections, from http://www.acousticreflections.com/ 6. Giorgio
Baldinelli.
(2019)
Building
Envelope.
Handbook
of
Energy
Efficiency
in
Buildings,
https://www.sciencedirect.com/ 7. John Calder. (Dec 20, 2018). What is Sound Diffusion (and Absorption)?, from https://www.acousticalsurfaces.com/ 8. Jisunfoo. (July 9, 2018) Auditorium: A Case Study on Acoustic Design Presentation. from, 9. https://www.slideshare.net/jisunfoo/ 10. Tian Jiun. (Jul 22, 2019) Auditorium: A Case Study on Room Acoustic, from https://issuu.com/locktianjiun/ 11. K.B.Ginn. Architectural Acoustics (Nov, 1978), from, https://www.bksv.com/media/doc/bn1329.pdf 12. Jana J. Madsen. (June, 28, 2006) Acoustics: Absorb, Block, and Cover, from https://www.buildings.com
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from
12.Acronyms RT- Reverberation time NRC- Noise Reduction Coefficient STC- Sound Transmission Class (STC is another helpful industry rating that can be used to distinguish which products are more equipped to block sound than others. A higher STC would mean that the panel would ‘block’ more sound and result in better privacy.)
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13.Appendix Definitions of Acoustic related terms Reflection: A direct sound from a source travels to the receiver without striking any surface. Within an enclosed environment, the direct sound also travels toward the surfaces and boundaries of the room. When the sound hits these surfaces, it is sometimes reflected back into the space.
Absorption: Sound absorption is the measure of the amount of energy removed from the sound wave as the wave passes through a given thickness of material.
Diffusion: A diffusive surface doesn't directly reflect or absorb sound, but scatters it in many directions. Diffusion is the method of spreading out sound energy with a diffuser for better sound in a space.
There are only two acoustical tools available to improve sound inside a room, whether that room is huge or tiny: sound absorption and sound diffusion. Both tools will improve sound perception in spaces that, if left untreated, would be a bad influence on the sound quality.
Reverberation: A reverberation, or reverb, is created when a sound or signal is reflected causing numerous reflections to build up and then decay as the sound is absorbed by the surfaces of objects in the space – which could include furniture, people, and air. This is most noticeable when the sound source stops but the reflections continue, their amplitude decreasing, until zero is reached. 50
Reverberation Time: Reverberation time is the time required for the sound to “fade away” or decay in a closed space. Sound in a room will repeatedly bounce off surfaces such as the floor, walls, ceiling, windows or tables. When these reflections mix, a phenomenon known as reverberation is created. Reverberation reduces when the reflections hit surfaces that can absorb sound such as curtains, chairs and even people. The reverberation time of a room or space is defined as the time it takes for sound to decay by 60dB. For example, if the sound in a room took 10 seconds to decay from 100dB to 40dB, the reverberation time would be 10 seconds. This can also be written as the T60 time. At the beginning of this century W.C. Sabine carried out a considerable amount of research on the acoustics of auditorium and arrived at an empirical relationship between the volume of the auditorium, the amount of absorptive material within the auditorium and a quantity which he called the reverberation time This relationship is now known as the Sabine formula: RT = 0.161 V / A Where, RT = the reverberation time defined as the time taken for a sound to decay by 60 dB after the sound source is abruptly switched off V = the volume of the Space in m3 A = the total absorption of the Auditorium in m2 A = α · S = equivalent absorption surface or area in m2 α = absorption coefficient or attenuation coefficient S = absorbing surface area in m2 A = α1 · S1 + α2 · S2 + α3 · S3 + ….
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Echo: If reflected sound is excessively delayed (for more than 70 milli sec.) after the direct sound is loud enough to be obstructive, it is clearly heard above the general reverberation, is called ‘Echo’ It is a sound that is repeated because sound waves are reflected back.
Attenuation: Sound attenuation is defined as the loss of energy from sound waves. Basically, attenuation is a damping of sound, an interruption that diminishes the volume and quality of the sound wave. Sound waves interact with different objects in different ways and sound quality is reduced more by some objects than others. Sound is created by oscillation of waves. Therefore, that means that attenuation, the damping of sound, comes from interrupting these waves. Sound is energy, so in a perfect environment, the oscillation of sound would only lessen naturally over space as the energy was depleted. This further weakening results from scattering and absorption.
Scattering is the reflection of the sound in directions other than its original direction of propagation. Absorption is the conversion of the sound energy to other forms of energy. The combined effect of scattering and absorption is called attenuation.
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